Cellulose aminomethanate sausage casings

ABSTRACT

A tubular film sausage casing comprising a cellulose aminomethanate wherein from 0.5 to 30 numerical percent of the cellulose hydroxy groups have been substituted with aminomethanate groups. The casing may be crosslinked or may be fiber reinforced.

This is a continuation of application Ser. No. 025,454, filed Mar. 13,1987, now U.S. Pat. No. 4,789,006, issuing Dec. 6, 1988.

BACKGROUND OF THE INVENTION

a) Field of the Invention

This invention relates to cellulose based products and more particularlyrelates to viscose type products which can be formed into sausagecasings.

b) History of the Prior Art

Viscose has been used for an extended period of time in the manufactureof regenerated cellulose sausage casings. The viscose, dissolvedmodified cellulose, which has been commercially used in the prior arthas almost universally been formed by treating cellulose with causticsoda and carbon disulfide to form cellulose xanthate which is thendissolved in weak caustic solution to form the viscose. The productsformed from cellulose regenerated from this viscose have found greatcommercial success. Unfortunately, the carbon disulfide used in theprocess and by-product carbon disulfide and hydrogen sulfide from theprocess are flammable and extremely toxic and these products must becarefully managed. Such management is made more complex when thematerial is a tubular material such as a sausage casing which canconduct gaseous products.

In addition, in the traditional viscose process for the manufacture ofsausage casings, regeneration of the cellulose is necessary.Furthermore, the resulting cellulose product does not lend itself tointernal plasticization and requires some kind of plasticizer forhandling. In the absence of some kind of plasticizer the product isbrittle.

A viable alternate to the traditional viscose process for themanufacture of sausage casings would therefore be desirable.

As early as 1930 (U.S. Pat. No. 1,771,461) it was proposed that ammoniaderivatives of carbon dioxide such as urea, could be reacted withcellulose to form soluble products which could subsequently be used forthe manufacture of fibers and films. This process was further discussedin U.S. Pat. Nos. 2,129,708 (1938) and 2,134,825 (1938) assigned ontheir faces to E. I. du Pont. The viscose type products resulting fromthis process are esters which will be referred to herein as celluloseaminomethanates, although they may also be known as cellulose aminoformates or cellulose carbamates in other references.

While the resulting final products, e.g. fibers and films, at least whenmade on a small scale, had fair properties, the properties, especiallypurity strength and solubility at comparable chain lengths, were notnearly as good as similar products made from conventional viscose, i.e.the xanthate process. Recently, in part due to increased awareness ofour environment, interest has again been shown in the alternate viscosetechnology disclosed in the above early references. It has, for example,been disclosed in U.S. Pat. No. 4,404,369 issued in 1983, that analkali-soluble cellulose derivative could be produced by treatingcellulose with liquid ammonia having urea dissolved therein. The objectwas to develop a product having urea distributed through the productprior to reaction by heating. The process described nevertheless hasproblems in that liquid ammonia also must be contained and in additionthe product still does not have properties as good as desired for manycommercial applications.

Various proposals have been made for increasing solubility of thecellulose aminomethanate product, e.g. U.S. Pat. No. 4,526,620 whereinexcess urea is used to increase solubility but simultaneously createsurea contamination and U.S. Pat. No. 4,530,999 where the chain length isreduced by radiation which unfortunately also decreases end productstrength.

It was proposed in European Patent Publication 178,292 published Apr.16, 1986, that an improved product could be obtained when an alkali-ureaimpregnated cellulose was washed with urea solution to remove hydroxideprior to heating to form the ester. While this provided some improvementin the properties of the resulting ester, uniformity and thus strengthespecially when large quantities of products were made, are still not asgood as desired to permit substitution for most xanthate type viscose inmost commercial applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sausage casing in accordance with the present inventionshowing sausage casing 10 comprising cellulose aminomethanate 12reinforced with fibers 14.

BRIEF DESCRIPTION OF THE INVENTION

It has now been unexpectedly found, that despite its shortcomings in theprior art, cellulose aminomethanate type viscose is particularlysuitable for use in the manufacture of cellulose type sausage casings.When manufacturing parameters are properly controlled, the use ofcellulose aminomethanate type viscose has a surprising number of goodproperties in common with xanthate viscose. In particular, it has nowbeen unexpectedly found that water uptake by the coagulated productcould be unexpectedly low compared to other cellulose ethers and estershaving a comparable degree of substitution and of the order of suchuptake by products made from xanthate viscose. Furthermore, coagulationrates and coagulation bath components can be similar to xanthateviscose.

In addition, it was unexpectedly found that the cellulose aminomethanateviscose can be coagulated to form a good film product withoutregeneration of the cellulose and that the retained aminomethanategroups act as internal plasticizers thus reducing the requirement for asmuch added plasticizers as in conjunction with sausage casings made fromxanthate viscose. It has further been found that such films, ifinitially formed in flat rather than tubular form, can readily be madeinto tubes.

Furthermore, it has been found that fiber reinforced sausage casingproducts made from the aminomethanate viscose can have strengthproperties comparable to similar products made from xanthate viscose.

It has also been found that, if desirable, the strength of sausagecasings made from aminomethanate viscose can be further enhanced byintroducing crosslinking or by otherwise increasing polymer size.

All of the above advantages are unexpectedly obtained through the use ofcellulose aminomethanate viscose to manufacture sausage casings inaddition to the advantage of eliminate of undesirable CS₂ and H₂ Sproducts associated with the cellulose xanthate viscose process.

In particular, the invention is a tubular film food, e.g. sausage,casing comprising a cellulose aminomethanate wherein from 0.5 to 30numerical percent and preferably from 2 to 15 numerical percent of thecellulose hydroxy groups have been substituted with aminomethanategroups. Desirably, the average degree of polymerization (DP) of thecellulose is from 300 to 650 combined glucose units. If desired, thecellulose aminomethanate polymer may be at least partially regenerated.The sausage casing primary gel after coagulation desirably only containsfrom about 300 to about 500 percent water by weight of celluloseaminomethanate.

The polymeric cellulose aminomethanate may optionally be fiberreinforced or may be crosslinked wherein a crosslinking agent is reactedto connect at least two of the cellulose hydroxy groups, at least two ofthe aminomethanate groups or at least one hydroxy group with at leastone aminomethanate groups. Desirably, there are between 0.1 and 10crosslinks per 100 glucose units in the cellulose when crosslinking isused. The finished sausage casing product may be provided in the form ofa shirred sausage casing or in the form of reelstock.

DETAILED DESCRIPTION OF THE INVENTION

The tubular film sausage casing comprises a polymeric celluloseaminomethanate which may or may not be partially regenerated.

Cellulose which is aminomethanated in accordance with the presentinvention may be represented by the formula: ##STR1##

One half of this formula, i.e. ##STR2## whether a dehydro derivative orwhether or not it is substituted at an --OH position is referred toherein as a glucose unit. The average degree of polymerization of acellulose (DP), whether or not it is aminomethanated at a hydroxyposition, is the average number of combined glucose units. The preferredaverage degree of polymerization is from 300 to 650. The average ofpolymerization can be expressed as DP_(W) which is the weight average DPor by DP_(V) which is determined by calculation from a viscositydetermination and correlates with DP_(W).

The cellulose aminomethanate is formed by reaction of cellulose withcertain amine oxygen containing compounds such as urea or biuret.

It is believed that the cellulose is aminomethanated in accordance withthe basic formula: ##STR3##

The isocyanic acid is believed to be generated at the time of reactionfrom urea or cyanuric acid or a similar compound, e.g. ##STR4## The ureamay be carried into the cellulose structure by a suitable carrier suchas liquid ammonia to more uniformly distribute the urea throughout thecellulose structure, as for example is described in U.S. Pat. No.4,404,369.

The polymeric cellulose aminomethanate utilized in accordance with theinvention to form the tubular film sausage casing desirably has from 0.5to 30 numerical percent of the cellulose hydroxy groups substituted withaminomethanate groups and preferably has from 2 to 15 numerical percentof the cellulose hydroxy groups substituted. Prior to formation of thesausage casing, the polymeric cellulose aminomethanate desirablycontains from about 3 to 30 numerical percent and preferably from about5 to about 20 numerical percent of the cellulose hydroxy groupssubstituted with aminomethanate groups.

This structure permits the cellulose aminomethanate to be dissolved andhandled in a manner similar to traditional viscose. A tubular filmsausage casing may then be extruded by known means and coagulated in amanner similar to traditional viscose coagulation. The coagulatedtubular film may be regenerated with a hot dilute concentration ofsodium hydroxide.

More particularly, the cellulose aminomethanate having at least 3numerical percent of the cellulose hydroxy groups substituted andpreferably at least 5 numerical percent of the cellulose hydroxy groupssubstituted may be dissolved in from about 6 to 10 percent sodiumhydroxide solution at about -5° C. The quantity of celluloseaminomethanate which can be dissolved in such a solution depends largelyupon the average degree of polymerization of the cellulose and upon thedegree of substitution (DS) of the hydroxy groups with aminomethanategroups as well as upon temperature. Desirably, from 6 to 10 percent ofthe polymeric cellulose aminomethanate can be dissolved by slurryinginto a 6 to 10 percent sodium hydroxide solution at 15° C. followed bycooling to subzero temperatures, e.g. less than about -4° C. The reducedtemperature will cause the cellulose aminomethanate to dissolve. Aftersolution the temperature may again be permitted to rise up to 10° C. orhigher.

The tubular film may be coagulated in baths similar to the baths used tocoagulate traditional xanthate viscose. The bath may, for example,contain a mixture of sodium sulphate and sulfuric acid. An example ofsuch a bath might contain from about 200 to 300 grams per liter ofsodium sulphate and from about 100 to 200 grams per liter of sulfuricacid. After coagulation, the tube is neutralized with acid.

Very surprisingly, the aminomethanate viscose after coagulation andwashing retains a low percentage of water in the primary gel whencompared with other ether-type modified cellulose compositions. Thequantity of water retained is very surprisingly similar to the quantityof water retained by traditional xanthate viscose after coagulation. Thequantity of water contained may be as low as from between about 300 toabout 500 percent water by weight of cellulose aminomethanate which issignificantly lower than other coagulated ether type or ester typederivatives of cellulose. "Primary gel" as used herein means thecoagulated and washed cellulose aminomethanate prior to initial drying.

The tubular film may then be dried and if desired, regenerated in adilute caustic soda solution, e.g. 1-2 percent NaOH at from 80° to 100°C. for from about 5 to about 20 minutes. Such a finished regeneratedcasing may contain as few as 0.5 numerical percent or less of thecellulose hydroxy groups substituted with aminomethanate groups.

It has further been unexpectedly found that the sausage casing film canbe formed from cellulose aminomethanate polymer, as previouslydescribed, which is fiber reinforced and which has characteristicscomparable to fiber reinforced xanthate viscose films. The reinforcingfiber may be any suitable fiber such as fibers made from organicpolymers and even inorganic fibers such as fiberglass. In general,however, it is most desirable that the fiber be physiologicallycompatible and is therefore most usually a cellulose fiber both forreasons of physiological compatability and cost. The fibers may beblended with the cellulose aminomethanate polymer prior to formation ofthe sausage casing or alternatively and preferably the celluloseaminomethanate may be extruded into a fiber web which is being formedinto a sausage casing. The fiber web may be either a felted or woventype web. In general, the web is a cellulose fiber paper and the casingcomprises such a paper impregnated with said cellulose aminomethanate.

The methods for impregnating such a paper are well known to thoseskilled in the art and in general follow the procedures previously usedfor cellulose xanthate type viscose. A description of such proceduresmay be found, for example, in U.S. Pat. No. 4,390,490.

It has further been found in accordance with the present invention thatsausage casings having increased tensile strength can be obtained bymeans of crosslinking. In particular, the cellulose aminomethanate in asausage casing may comprise a plurality of crosslinks wherein each ofthe crosslinks are formed by a crosslinking agent reacted to connect atleast two of the cellulose hydroxy groups, at least two of theaminomethanate groups or at least one hydroxy group or at least oneaminomethanate group. A crosslinking agent may be any effectivelydifunctional compound which will react with aminomethanate or hydroxygroups in the cellulose aminomethanate polymer.

The number of crosslinks in the cellulose aminomethanate polymer sausagecasing preferably ranges between about 0.1 and 10 crosslinks per 100glucose units in the cellulose. A crosslinking agent may be anyeffectively polyfunctional compound which will react with aminomethanateor hydroxy groups in the cellulose aminomethanate polymer. Acrosslinking agent may, for example, therefore be selected from thegroup consisting of polyfunctional compounds containing at least twogroups selected from aldehyde, amine, carboxy, alkylhalide, acidhalide,methylol, carboxylic anhydride and isocyanate groups. Especiallydesirable crosslinking agents are long chain crosslinking agents, whichhave been found to increase strength while minimizing embrittlement,which are potentially physiologically acceptable even though they arereacted into the system which prevents physiological absorption.Examples of preferred crosslinking agents therefore, for example,include glutaraldehyde and melamine formaldehyde type resins whichcontain a high methylol content to provide the reactive crosslinkinggroups.

"Long chain" as used herein means that the crosslinking agent containsat least 5 and preferably more atoms in the molecular chain between thereaction sites.

It should be noted that crosslinking of prior art regenerated cellulosefrom xanthate viscose for sausage casing, has been unsuccessful sincethe product usually comprises an impractically brittle film which inmany cases has reduced, rather than increased tensile strength. Theincreased embrittlement or decreased elongation at break resulted inpoor toughness and was unsuitable for use as a packaging or casing film.

It has been unexpectedly found that sausage casings made from celluloseaminomethanate polymer as described herein is not as subject toembrittlement by crosslinking as is traditional xanthate viscose. Whilenot wishing to be bound by any particular theory, it is believed thatsince the cellulose amino-methanate has a low density of very uniformlyspaced aminomethanate groups, the crosslinkage is not as detrimental tothe elongation at break as is the case with conventional regeneratedcellulose film. This effect is even further reduced when long chaincrosslinkers are used as is previously described.

The use of glutaraldehyde, which was freshly diluted and used within afew hours of solution, suggests that a substantial increase in burststrength of the cellulose aminomethanate film can be obtained whileretaining sufficient elongation at break. While there is some reductionin elongation at break and this reduction is not desirable, suchreduction of elongation at break was tolerable and to a degreedramatically less than has been previously experienced in previousresearch on crosslinking traditional xanthate viscose cellulose casing.

It has been further unexpectedly discovered that if a low percentage ofa long chain crosslinker such as glutaraldehyde is used, very largeincreases in tensile strength and burst strength of the resultingsausage casing film can be obtained with tolerable reductions in breakelongation. Such a low loading or percentage of crosslinking agent canfor example be obtained by steeping the gelled aminomethanate film inacidic solutions of 2,500 to 5,000 parts per million of glutaraldehydeor 2,500 to 5,000 parts per million of high methylol content melamineformaldehyde. In particularly sensitive systems, other conditions may beused, e.g. even lower concentrations of crosslinkers, longer chaincrosslinkers and different reaction conditions.

The cellulose aminomethanate polymer sausage casings of the presentinvention can be handled and packaged in a manner similar to traditionalxanthate viscose regenerated cellulose sausage casings. Such sausagecasings can, for example, be provided as reelstock or can be shirred andsold as shirred sticks. Methods for forming such shirred sausage casingsare well known to those skilled in the art as, for example, is taught inU.S. Pat. Nos. 3,454,982 and 3,456,286.

The following examples serve to illustrate and not limit the presentinvention.

Various cellulose am aminomethanates were prepared substantially inaccordance with the teachings of U.S. Pat. No. 4,404,369. Cellulose pulpwas saturated with urea dissolved in liquid ammonia, the ammonia wasevaporated and the fibers containing 50 to 100% urea on the fiber weightwere heated to 165° to 175° C. for periods of one to three hours. Theresulting product was then extracted with hot water to remove excessurea and biuret to obtain a 0.06 to 0.25 DS cellulose aminomethanatewhich will readily dissolve in 8 to 10%, -5° C. sodium hydroxide. DS asused in these examples means the number of --OH groups substituted perglucose unit divided by three (available --0H groups). Numerous suchpreparations were made.

In particular examples, various preparations were made using cellulosepulp regenerated from alkali cellulose. Details of some of suchpreparations are as set forth in the following examples.

EXAMPLE I

220 g of cellulose which had been derived from a neutralized alkalicellulose (AC) crumb was used. The alkali cellulose crumb was made froma 1500 DP_(W) prehydrolized sulfate dissolving wood pulp which had beensteeped, mercerized, shredded and aged at 28° C. for 33 hours.

220 g of this aged AC crumb fluff was immersed in a dilute solution ofurea in liquid ammonia at about a 1-10 liquor ratio for 2 hours near theboiling point of the liquid ammonia. The resulting pulp was then pressedwith removal of the liquid ammonia by tumbling the material at slowtumbling rate in a cylinder sparged with dry air to assist in removal ofthe liquid ammonia. The tumbling was continued 21/2 hours to give 307 gof the urea impregnated cellulose which had approximately 44% load ofurea based on the weight of the cellulose.

Several portions of the urea impregnated cellulose were converted into50 g disks of density of about 0.7-0.8 g per cc by loading a 7 oz. panof aluminum with the 50 g of pulp, placing an aluminum foil over theassembly and then pressing in a pellet press with wood blocks at a20,000 lb. load on the ram to give a disk approximately 1/4" thick.

The disks were placed in a stainless steel tray and heated in an oven at105° C. for preheating the disks to near 105° C. temperature. The diskswere then rapidly introduced into an oven set at 202° C. which droppedthe air temperature to 192° C. The disks were then cured for 15 minuteswith the higher temperature rising to about 200° C. in 9 minutes. Theresulting disks were then broken up and washed in hot water and testedfor solubility in cold 8% sodium hydroxide solution.

A 6% dope of the disk-cured cellulose aminomethanate was made in theusual manner by adding the solid to precooled -5° C. 8% sodium hydroxidecontained in a beaker with a laboratory high shear mixer and dissolvingthe material over a period of about 2 hours. A clear solution arose. The400 g of 6% dope was then centrifuged 1 hour at about 2700 rpm to removeair and any traces of fiber fragment. This particular dope was stored ina refrigerator at 6° C. for approximately 24 hours prior to use to makefilms which, in turn, were used for subsequent cross-linkingexperiments.

EXAMPLE II

A 33 hour aged AC crumb derived cellulose as previously described wasused as a starting material. Approximately 150 grams of urea wasdissolved in 5500 ml of liquid ammonia at -49° C. and warmed to about-43° C. The solution was used for saturating approximately 400g of thepulp "as is" by adding the pulp in portions to the solution and pressingwith a spatula to impregnate the pulp completely as it was added. Thepulp was furthermore pressed 3 times within the next 45 minutes toassist in uniformity of impregnation. The steeping time was 45 minutesbefore the solution was decanted. The solution showed approximately 3%concentration of urea at this point. The urea-impregnated pulp wastumbled at room temperature with a 2 psi dry air sparge through thetumbler to aid escape of ammonia. A 535 g yield of the dry material atroom temperature was obtained. The urea loading was approximately 36%based on the weight of the cellulose.

Approximately 150g of this 36% addon urea cellulose was placed instainless steel shallow tray and pressed with the hands to approximately1/2" thickness. The contents of the tray were preheated for 1 hour in a105° C. oven and then quickly placed in a laboratory oven placed at 200°C. and allowed to cure for 13 minutes. Large amounts of ammonia wereevolved.

The crude product weighed approximately 141 g and was washed in hotwater and dried before use in making the cellulose aminomethanate dope.

A 6% dope of the resulting 350 DP_(V) aminomethanate was made bydispersing at -5° C., in 8% caustic and stirring with a high shearlaboratory mixer for 2 hours at temperatures from -5° to 0° C. The dopewas then centrifuged for 1 hour in a high speed laboratory centrifugeand was used without subsequent aging for making the 22 mldrawdown-derived gel films of Example VI.

EXAMPLE III

Example II was essentially repeated to obtain a 38% addon ureacellulose. The approximately 38% loaded urea cellulose was cured inseparate curing batches at 50g per batch. The 50g was pressed out as auniform layer in a 541 ×8" stainless steel tray and preheated to 105° C.for 1 hour prior to cure. The tray and contents were then placed in a200° C. set laboratory oven and allowed to cure for 12 minutes. A secondbatch was treated similarly and a third batch at 75g was also cured for12 minutes. The three batches were composited to make material for usein the preparation of 7% dope.

The dope was made by adding the 28 g of the polymer to 372 g of 8%caustic initially at -8° C. Very fast dissolution took place underlaboratory mixing. The stirring was done for 1 hour with a finaltemperature of 6° C. because of the heat of stirring. The clear dope wascentrifuged at 3000 rpm in a Beckman TJ6 laboratory centrifuge to removeair prior to dope casting.

EXAMPLE IV

Cellulose aminomethanate was also made substantially by the procedurestaught in U.S. Pat. Nos. 2,129,708 and 2,134,825 and in European PatentPublication 178,292 except that aqueous ammonia was used.

Forty grams of urea is blended with 200 ml 28-30% aqueous ammonia and3.6 grams of cellulose pulp. The swelled mixture is shaken for 30minutes and filtered and pressed. The resulting pad weighed 11.2 gramsincluding residual water and weighed 4.92 grams after drying overnightat 80° C. (in a vacuum). The dry pad was calculated to have a 37 weightpercent urea add on. The dried pad was then heated to between 160° and180° C. for about two hours. The resulting cured celluloseaminomethanate pad was soaked in ice water, macerated in a high shearblender, and filtered. The filtered material was then dissolved in -2°C. NaOH (9%) containing 1% ZnO. The resulting viscous solution wascentrifuged and cast into a film, coagulated, washed and dried. An IRspectra confirmed the presence of the aminomethanate group.

Similar results are obtained when NaOH solution is used instead ofaqueous ammonium hydroxide.

EXAMPLE V

Six percent of cellulose aminomethanate prepared as in Example I wasdissolved in dilute caustic solution and drawn into a 26 g/m², 22 milthick film. The resulting film was coagulated in a bath containing 140g/l H₂ SO₄ and 240 g/l Na₂ SO₄ for 6 minutes at 28° C. The coagulatedfilm was then washed. The film was then treated with a 2500 ppmglutaraldehyde, 0.2% malic acid solution, pH 2.8 crosslinking solutionfor 5 minutes. The film was then cured at 145° C. for 7 minutes. Theresulting film has an average burst strength of 14.7 psi as comparedwith an 11.1 psi burst strength for the same film which is not treatedwith the crosslinking glutaraldehyde solution. The crosslinking resultedin a 32% average increase in burst strength. The film can be readilyformed into a seamed tube which can be stuffed with meat using a 69%ZnCl₂ solution to adhere the seam. The resulting seam is strong andcontiguous.

EXAMPLE VI

Example V was repeated except that cellulose aminomethanate preparedessentially in accordance with Example II was used and a better solutionwas obtained. The film had an average burst strength of 14.7 psi ascompared with 10.0 psi for the same uncrosslinked film representing a47% increase in average burst strength. The film can readily be formedinto a seamed tube using a 69% ZnCl₂ solution to adhere the seam. Theresulting tube can be stuffed with meat.

EXAMPLE VII

Example V was repeated except that a 7% solution of celluloseaminomethanate prepared substantially in accordance with Example III wasformed and drawn into a 34 g/m² film. Additionally, 5000 ppmglutaraldehyde was used in the crosslinking solution. The resulting filmhad a 21.2 psi average burst strength when compared with a 13.0 psiburst strength for the same uncrosslinked film. This represents a 63%increase in burst strength. The film could readily be rolled and formedinto a seamed sausage casing using 69% ZnCl₂ solution to form the seam.

EXAMPLE VIII

Example VII was repeated except that a much thinner 18 g/m² film wasformed. The average burst strength was 15.8 psi when compared with only9.5 psi for the same uncrosslinked film.

EXAMPLE IX

The above films showed an increase in rewet burst strength but areduction in conditioned tensile strength. It was, however, found thatwhen proper conditions were selected an increase in tensile strengthcould also be obtained especially the tensile strength of rewetted film.

A 7% solution of 1.7%% N content 550 DP cellulose aminomethanate wasprepared in 8% NaOH. The solution was centrifuged at 1200 for 11/2hours.30 mil drawdowns gave 41-45 g/m² films which were coagulated for 8minutes in a 28° C. solution of 17% ammonium sulfate -5% sulfuric acidsolution. The films were then water washed. A film was steeped in aged2500 ppm glutaraldehyde solution at pH 2.8 for 10 minutes and cured at135° C. for 7 minutes. The resulting film had a tensile break at 12,270psi dry and 3,315 psi wet as compared with the same uncrosslinked filmat 9,870 psi dry and 1,390 psi wet.

EXAMPLE X

Example IX was essentially repeated except that high methylolmelamine-formaldehyde (MF) was used for crosslinking in a 5000 ppm MF,1000 ppm malic acid crosslinking solution. The film was steeped in thesolution for 10 minutes at 25° C. and cured for 7 minutes at 135° C. Theresulting film had a dry break at 10,140 psi as compared with 9,869 psifor the uncrosslinked control and a wet break at 2,607 psi as comparedwith 1,391 psi for the uncrosslinked control.

EXAMPLE XI

Example X was repeated except that 2500 ppm of MF was used. The drytensile strength was 12,803 psi and the wet tensile strength was 1,748psi.

EXAMPLE XII

Example I is substantially repeated except a 699 DP cellulose pulp(determined by viscosity test) aged as alkali treated cellulose crumb 16hours at 28° C. was used. 60 grams of the pulp was steeped in a solutionof 60 grams of urea in liquid ammonia at -40° C. for 2 hours. The excessis pressed from the steeped pulp and the treated pulp is tumbled for 15minutes. Excess ammonia is allowed to evaporate for 18 hours. Theresulting product is found to have a 58% urea add on. 50 grams of theproduct is cured and heated to between 185° and 190° C. for 15 minutes.

A 5% dope is dissolved in 8% caustic at -5° C. to 6° C. The product isthen centrifuged for 2 hours. A paper web is then impregnated with theliquid product and the product is coagulated as previously described.The impregnated web is then dried at 100°-105° C. for 10 minutes. Thereinforced product is found to have properties similar to the fiberreinforced xanthate viscose products traditionally used in the priorart.

EXAMPLE XIII

A prehydrolized dissolving high α sulfate pulp of 1500 DP_(W) (BuckeyeV-5) was steeped in normal steeping caustic at room temperature andshredded and without aging was neutralized and acetic acid washed anddried at low temperature. Resulting crumb derived cellulose from a woodpulp dissolving pulp had a DP_(V) of 957. This material was used as astarting material for cellulose aminomethanate synthesis. 53 g "as is"of the crumb was placed in a 7 cm diameter large mesh wire basket andvery lightly packed for immersion into the liquid ammonia solution ofurea. The basket was inserted into a mixture of 1650 ml of liquidammonia plus 90 g of urea at -45° C. The temperature went up because ofthe heat capacity of the cellulose. The cellulose was allowed to steepin this liquid for 30 minutes with occasional light pressing with aspatula to give good contact between liquid ammonia solution and thecellulose. The basket was removed and manually pressed lightly and thenthe excess liquid ammonia was evaporated under aspirator vacuum with a60° C. water bath for 2 hours and then the resulting urea impregnatedcellulose removed from the basket, placed in shallow trays and allowedto evaporate in a hood over night at room temperature. The resultingurea cellulose gained approximately 33.6% of its weight with urea. Itwas a white crumb like material.

The 70.8g of the urea impregnated cellulose was layered into twostainless steel Crays at approximately 2-3 mm layer of material. Placedquickly into a laboratory oven initially at 200° C. The oven cooled toapproximately 177° C. as a result of the introduction of the sample andthe sample was allowed to cure for 15 minutes. The oven increased to186° C. at the end of the cure. The resulting high DP celluloseaminomethanate had a very light but a very uniform tan color after cure.The crude material weighed 63.2 g after cure and after hot water washingweighed 47.2 g. The resulting cellulose aminomethanate had a nitrogencontent of about 1.4% and a DP_(V) of 545.

Because of the high molecular weight of the cellulose aminomethanate, a4% solution of the material was made in -5° C., 8% sodium hydroxidesolution. The solution was made by rapidly introducing the high DPcellulose aminomethanate into the cooled dope and immediatelydissolution was noted to occur with the dope increasing in viscosityvery rapidly. The dope was stirred with a high shear laboratory mixerfor 1 hour. The 300 g batch was then centrifuged to remove air and asmall amount of undissolved fibers.

The resulting dope was a very light and viscous dope which was suitablefor purposes of hand casting the dope into film. The 4% solution ofpolymer was beaded onto a plate glass plate and 30 ml draw down donewith hand cast drawbar. The resulting dope layer was converted to acellulose aminomethanate film by introducing the plate and liquid filminto a typical Muller type coagulation and neutralization bath. The bathwas held at 25° C. It contained approximately 140 g per liter ofsulfuric acid and about 250 g of sodium sulfate. It was noted the filmscoagulated within 3-5 seconds and were allowed to remain in the bath for5 minutes to assure complete precipitation of the primary gel from thedilute polymer dope. The transparent, clear, almost colorless tough gelfilm was removed after it had floated from the plate in about 1 minute.It was removed from the bath, washed in tap water and then washed indeionized water briefly to remove traces of salts from the tap water.The films were dried on nylon hoops at room temperature to give clear,tough films. The films had a thickness in the 80% conditioned relativehumidity (RH) state of approximately 0.8 Mil. The resulting films showeda 80% RH conditioned tensile of about 5500 psi at a elongation break ofabout 70%. The rewet tensile was approximately 1230 with a rewetthickness of approximately 1.4 Mil. The elongation at break rewet wasabout 30.7%.

It is known that the use of a dilute dope solution in hand casting givesrise to poorer films then the use of a more concentrated solution underotherwise similar conditions of film casting. The viscosity of the doperequired a low polymer concentration for simple hand casting procedures.However, with different equipment a somewhat larger dope concentrationcould be managed.

When the centrifugation time of the 4% dope was extended to 3 hours at2700 rpm, the break tensile at 80% RH increased to 6685 psi, breakelongation was 13%, and break force was 6.89 lb/inch. A 3% dope gaverise to a 0.5 ml thick final film, which had a break tensile of 7515, a12.9% elongation at break and a 3.98 lb/inch break force. The additionalcentrifugation did improve the tensile strength. Visually, the morecentrifuged dope was clear. The material appeared to be quite tough,even without the use of a conventional plasticizer.

EXAMPLE XIV

A high quality 96.5% alpha content 635 DP_(W) dissolving wood pulp wasused as starting material.

A batch of 450 g of the dissolving pulp was fluffed to make it moreaccessible, was added to 5.8 liters of liquid ammonia plus 214 g of ureacontained in Dewar flask at approximately -40° C. The fluffed materialwas compressed periodically during the 2 hour steep and manuallysqueezed and drained to remove 705 g or 950 ml of the liquid ammoniasolution.

The batch was then placed in a rotating polyethylene drum of about 20"diameter for tumbling during the evaporation of the liquid ammonia. Thetumbling required about 3 hours to get to a 624 g net weight for theresulting urea-impregnated cellulose which then contained approximately38% addon to the cellulose. The material had 6% volatiles defined asthat which is volatile at 110° C. for 3 hours drying time for thesample.

The above and similar batches were accumulated to do a large scalecuring of this low addon, low DP cellulose material to form a low DPcellulose aminomethanate suitable for use as an impregnating liquid fora hemp fiber reinforced film.

The resulting 1160 g of the urea impregnated cellulose, containing35-36% urea addon, were placed in stainless steel trays in approximatelya 5 cm thick layer at a pack density of about 0.12 g per cc. Athermo-couple was inserted into the midpoint of the thickness of one ofthe trays and the tray placed in a large laboratory oven for cure. Thetrays were placed in the oven initially set at about 130° C. and theoven went to about 110° C. as the trays were placed in it. The oventemperature was then rapidly raised while the temperature of themidpoint of the probe in the pad was followed and the oven raised at alevel to permit no higher than 40° C. differential in temperaturebetween the oven and midpad temperature for any midpad temperature inexcess of 120° C. A midpad temperature of 120-158° C. the averagetemperature differential was 40° C. The total cure time was 43 minutesfor the batch. The batch was then removed and exhibited a light tancolor which was uniform throughout the thickness of the 5 cm pads.

The resulting aminomethanate was washed in hot water to removeby-product materials and dried at low temperature to approximately 3%moisture. Approximately 845 g of pure cellulose aminomethanate with anitrogen content of 1.24% resulted. This material when dissolved in 8%caustic at 8% polymer concentration showed a ball fall of viscosity ofapproximately 17 seconds. This viscosity is suitable for a dope to beused in impregnation of a reinforcing web to make reinforced casingmaterial. The 7% dope centrifuged at 2700 rpm for 1 hour showed noobvious residue of fibrous at the bottom and was air free from thecentrifuging process.

An 8 Kg batch of 7% aminomethanate solution was made in 8% sodiumhydroxide using a jacketed planetary laboratory mixer. Theaminomethanate was added to the port of the mixer which had in it a mixof 4932 g ice and 2480 g of 25% cooled sodium hydroxide solution. Thetemperature of the dispersion of aminomethanate was initially -6° C. Themixing was continued near full speed for about 11/2 hours with thetemperature allowed to rise gradually to 0° C. The dope was thenfiltered at 50 psi through a 100 micron filter. A yield of about 7.2 kof filtered dope was obtained, the remainder being the mechanical lossin the pressure feeding device and in the void space of the filtercasing.

The resulting filtered dope was placed in a 4° C. refrigerator and thedope was drawdown with 30 mil drawdown and 22 mil drawdown blades forthe manufacture of abaca web reinforced films.

At 20° C. the material was drawn down on a glass plate and a 121/2 basisweight abaca web was immediately placed on the drawdown liquid andallowed to saturate with the liquid for 1 minute. The web was rapidlysaturated with the aminomethanate dope and the resulting plate andattached film was then placed in a modified fibrous casing coagulatingbath for 10 minutes at 20° C. This was enough time for coagulation andneutralization for the caustic in the bath. The resulting reinforcedcellulose aminomethanate films were then washed in hot tap water untilfree of acid. The coagulation liquid contained about 8% ammonium sulfateabout 12% sodium sulfate and 6% sulfuric acid. The resulting reinforcedgel films were dried on hoops for 10 minutes at 135° C.

The product showed a rewet tensile strength of 3144 psi and anelongation at break of 69% at 30 mil and 3038 psi tensile and 59.8%elongation at 22 mil.

Crosslinking with glutaraldehyde at high concentrations, i.e. 2500 or5000 ppm was not effective to improve the properties of these reinforcedfilms. It is, however, believed that improved properties can be obtainedunder different conditions, e.g. long chain or polymeric crosslinkers,different concentrations and different reaction conditions

EXAMPLE XV

A pilot run was made using approximately 12 gallons of 6% celluloseaminomethanate dope that had been filtered through a 60 micron 200 in²filter and had also been deaired. The size 1 casing run was done atnormal commercial running rate of 30 ft per minute.

The 12 gallons were made up of 5 separate aminomethanate preparationswhich were slightly different in composition and DP. These are describedas follows:

The first 4.5 gallon batch, 6% aminomethanate dope was made from anaminomethanate synthesized from DP_(W) 660, 93.4α, dissolving pulp(Buckeye V-65) that had been steeped in dilute urea solution and liquidammonia for 2 hours to build a 45% load of urea based on the weight ofthe cellulose. The steeping was done at 1:10 ratio, excess liquid pouredoff, the pulp fluff slightly squeezed, and then tumbled for about 21/2hours in a horizontal tumbling device with a 2 psi air flow through thesparging device to aid in evaporation of ammonia at near or below roomtemperature. The resulting white fluffy material was then converted tothe cellulose aminomethanate by use of 2-3 cm layers of the compactedmaterial placed in stainless steel trays and cured in a laboratoryvacuum oven.

The oven was set at 156° C. and the stainless steel trays with the ureacellulose pads were introduced which dropped temperature to 130° C.Curing was continued at 23" mercury vacuum from an aspirator with asmall air stream flowing through the oven both to sweep ammonia away andto aid in heat transfer. The curing was continued for 21/2 hours withthe air temperature near the 155° C. for 2 hours of that period. Theresulting cured crude cellulose aminomethanate was light tan in colorand was washed in hot water extensively to remove by products and driedat low temperature to avoid hornification, i.e., undesirable filmsurface densification.

A 7% solution in -5° C., 8% sodium hydroxide was a fairly dark brown,very clear solution. It was thus judged that this material would besuitable for the matrix in the fibrous casing run.

For dissolving, a jacketed insulated planetary mixing device of 4gallons capacity was used with 900 g of pulp prewet with ice water priorto introduction into the mixer. The requisite amount of water in theform of ice, and sodium hydroxide in the form of 25% sodium hydroxidewere previously introduced into the mixer and the mixer cooled to about-6° C. The ice water wet-pulp with the appropriate adjustment to give a6% final polymer solution was introduced through a port and mixingcontinued at -5 to -2° C. for 21/2 hours. The dope was deaired byapplication of a vacuum for the last hour of the dissolution. A clearviscous dope resulted which could be filtered through about a 210 squareinch, 60 micron filter with approximately 1 hour required for filtrationof the total batch.

The filtered and deaired, dope was maintained at approximately 0° C. forthe succeeding day.

A second 4 gallon batch of 6% cellulose aminomethanate dope was madefrom a carbamate derived from about 2/3 of the 900 g of V-65 Buckeyepulp and 1/3 DP_(W) 855-930, 94.6% α dissolving pulp (Buckeye V-60). Thecellulose aminomethanate was synthesized in a vacuum oven starting outat about 10° C. more than the previous batch and with reaction time of21/2 hours. The material was washed and dried at low temperature priorto dissolution in the jacketed ross planetary mixer.

In this dissolution, the 900 g of bone dry aminomethanate was presoakedin 3600 g of ice water for 1/2 hour. The mixture of ice and sodiumhydroxide in the mixer was set initially at -8° C. before addition ofthe cold wet aminomethanate. The mixer was operated at top speed ofabout 160 rpm for 2 hours and the contents observed to contain someparticles. An additional one hour resulted in no particles at atemperature of 2° C. The batch appeared to be less viscous than thefirst batch and better quality. A 60 micron filter with approximately210 square inch filter area was used for filtration. The filtration wasaccomplished after a one hour deairation of the batch during thisdissolution process. The resulting filtered and deaired dope wasretained for admixture with the remainder of the dope for the pilot run.

A third batch was made of 6% cellulose aminomethanate dope. In this casea mix of 1/3 Buckeye V-60 derived carbamate and 2/3 DP_(W) 635, 95.5 αdissolving pulp (Buckeye V-68) derived aminomethanate was used. Theaminomethanate had been made from cellulose with a load of about 45%urea and the curing of the urea impregnated cellulose to convert tocellulose aminomethanate was done under atmospheric pressure rather thanin a vacuum oven. The curing was done in a relatively low air flow ratelaboratory oven.

The urea cellulose was loaded into stainless steel trays at about 5 cmthickness with a density of about 0.13 g per cc. The oven was initiallyset at 140° C. with the trays at room temperature introduced into theoven cooling it to 125° C. The oven was gradually programmed to increasethe temperature as the temperature of a thermo-couple set midway down inthe pad increased in temperature. For temperatures below 120° C. thetemperature differential could be 70-80° C. For temperatures above 120°C. the maximum temperature differential allowed was 60° C. The reactionwas continued for a total of 75 minutes with the pad temperature at162-168° C. for the last 25 minutes.

The air temperature maximum was 200° C. and at 45 minute reaction timewas reduced gradually to 170° C. to avoid continued escallation of thecuring temperature. A very uniformly tan colored series of pads wasgotten with a uniform color throughout the thickness of the 5 cm pad.The material was washed in hot city water at 50-55° C., was pressed freeof excess water and dried at 65-70° C. to avoid hornification. Thismaterial was the starting material used in the preparation of the thirdbatch of dope to be used in the pilot scale run.

The composited, filtered, deaired dopes had material with about a 1.4%nitrogen content based on the weight of the dry cellulose aminomethanateat the time it was introduced into a blow tank to feed the die of afibrous casing pilot machine. The die used was a pressure-fed diewherein a 121/2 pound basis weight per 2880 square feet abaca saturatedtissue web was impregnated using a hydraulic wedge principle and anenclosed die which forced the liquid into the paper and did not dependon spontaneous capillarity to impregnate the web uniformly with theaminomethanate dope. The dope was fed to the machine at about 10° C. sowas quite viscous.

The die was adjusted using a paper leader to avoid wastage of the verylimited amount of cellulose carbamate dope. The coagulation bath wasmodified over that commonly used for cellulose fibrous casing and wasrun at 45° C.

The coagulation bath consisted of 142 g per liter sulfuric acid and 253g per liter sodium sulfate initially. The pilot machine was run at 30feet per minute and the time of contact of the extruded, impregnatedpaper with the coagulation bath was less than 10 seconds. It was notedduring the start of the run that the cellulose carbamate 6% dopecoagulated very rapidly, such that when the casing was pulled throughthe set of 8 wiper rods just above the coagulation tank, that no damageto the film seemed to occur. Some problems were encountered in making a1/4" lap seam initially, but subsequently casing was made wherein theseam held. The casing was washed with one tank past the regenerationtanks and with only three wash tanks prior to the normal position of theglycerine plasticizer tank. The casing was readily made to the flatwidth standards of 6.2 to 7.1 cm and part of it, approximately 200 feet,was passed through to the dryer. All the gel casing samples wereretained so that links of the casing that had a good seam could be driedas 4 feet lengths in the laboratory high air velocity oven. The casingwas almost colorless and it was noted that the fresh gel film just abovethe coagulation tank when soaked in water at about 1-10 liquor ratio hada pH of about 2.4. Clearly, even the 10 second coagulation time wherethe coagulation had access to both the inside and outside of the film,resulted in the neutralization of essentially all of the caustic in the6% aminomethanate.

Since no gases were evolved, no problems in distortion of the gel casingduring passage to the machine were noted. The osmotic water would betaken up, due to the salt in the film, but appeared to present noproblems and a normal cut cycle was maintained during the approximately45 minute production run. The resulting casing samples having a glycerolcontent to about 10% had a Mullen rewet of about 35 psi, whereas the gelhad a Mullen of about 16% psi. This behavior was also fairly typical ofhand cast aminomethanate fiber paper-reinforced films.

The casing had a bone dry gauge of approximately 85 g per 10 meters,which is somewhat lower than the 94 g per 10 meters that would betypical of a size 1 cellulose based casing. However, the cellulose basedcasing would be made with 7.7% cellulose xanthate viscose, compared with6% cellulose aminomethanate dope employed in the current pilot run.

The cellulose aminomethanate in the matrix casing expressed on a drybasis had a nitrogen content of 0.7% at the dry end of the dryer. Thisrepresents loss of 50% of the initial nitrogen content in the mixed dopebatched during the first day storage and the handling of the dope at thecasing process machine.

The loss in aminomethanate during storage and prior to extrusion isprobably good because this reduces the alkali swellability of the filmand thus gives a stronger film.

A sample of casing retained in the gel state after the pilot run showeda gel 16 psi average Mullen test; whereas the rewet casing showed a 31psi Mullen. The somewhat lower Mullen strength than that for standardsize 1 commercial xanthate viscose fibrous casing can be attributed tothe lower bone dry gauge of this casing relative to commercial xanthateviscose size 1 casing.

A meat emulsion representing a commercially made meat material was usedto stuff the size 1 casing to a circumference of 6" which is standardfor this size casing. The cooking was done in a laboratory style ovenwith no RH control. The oven was initially set at 75° C. and thebolognas cooked for 135 minutes to internal temperature of 73° C. Thecooked sausage looked normal.

To further test the casing, a length of casing was hand shirred on amandrel without casing damage.

What is claimed is:
 1. A tubular film fiber reinforced sausage casingcomprising an at least partially regenerated polymeric celluloseaminomethanate having from 0.5 to 30 numerical percent of hydroxy groupsin the cellulose substituted with aminomethanate groups prior to beingregenerated.